I just found out about the "enemy of Sauron" character trait and was wondering what exactly its effects/mechanics might be in the game.

Here's a quote from the Adventurer's Companion:
"All creatures of any kind recognise you as an enemy of Sauron. His servants fear you, and will avoid confronting you, unless confident in their superiority. When facing proof of the presence of the Enemy, you cannot refrain yourself and must take action."

By invoking this trait, would it be possible for a Noldor character to resolve an enemy encounter and force adversaries to retreat unless they are absolutely certain that the fellowship cannot beat them in a fight?

How would you handle such a situation? Whould you consider certain prerequisites for the trait to be invoked/have an effect or maybe tie it to certain rolls/skill checks?

Any comments and thoughts are much appreciated!
Oh and please bear with me if I sound a little funny at times - English is not my native language.

I think (and I might be wrong) the idea with this trait being invoked is in the opposite kind of situations. I think it would be more suitable to use it for example when meeting a group of rangers or elves or whatever in Eriador and they recognize you to be an enemy of Sauron so they act friendly towards you rather than invoke it against a group of orcs and force them to flee from you.

Of Finarfin's children I am the last. But my heart is still proud. What wrong did the golden house of Finarfin do that I should ask the pardon of the Valar, or be content with an isle in the sea whose native land was Aman the Blessed? Here I am mightier.

The wording certainly suggests to me that this is used in the way that the OP describes rather than what Farinal has suggested. That said, it’s a trait and it would be perfectly reasonable imo to invoke it to confirm your status to ‘friendlies’.

I would tend to be literal in my interpretation when it comes to confrontations with the enemy. It is the character himself who is the Enemy of Sauron and not the entire Fellowship. His status will not prevent a goblin attack on the Fellowship. However, in circumstances where there is outnumbering on the Enemy side and the LM assigns the combats, the Enemy of Sauron is likely to be avoided by all but the most capable of the foes (or a big dumb brute). He might also find himself unduly targeted by archers and the like.

It has to be remembered though that this only applies to servants of Sauron.

I guess that this might equate him to a combined ‘Captain and Champion’ of the Fellowship.

You can invoke a trait to automatically succeed at a common skill, subject to LM's approval. Last I checked "Cause Enemies to Flee" is not a common skill.

However, if the player declares his or her intent to "reveal my wrath" (or whatever) and the LM asks for an Awe roll, then sure I could see the player asking if the trait can be invoked for an automatic success.

I played a Noldor Elf with this trait, I didn't get a whole lot of use from the trait. But that doesn't mean you can't get some use from it. Like others have said you could use this trait to confirm your character's dedication to the free people's as a sworn enemy of the Sauron. So you could activate the trait for Courtesy, Persuade tests when speaking to other people who are sworn enemies. To convince any of the Wizards of your dedication, groups of Elves, Rangers, Beorn, Dwarves perhaps. As a loremaster I would let players activate the trait for the intimidate foe action, for an auto success or to gain AP.I would also rule that the character knows old lores about Suaron. They may be able to speak a bit of the black speech, and would understand much about the First Age when it came to Sauron, Morgoth, Balrogs, The corruption of Numenor, The creation of the Rings of Power. (Not how to create Rings of Power, but the history. I would let them use it for Batte tests. I would also let players use it with the Rally/Enhearten Comrades action.

So with all that said we already have a nice list of skills that the trait can be used with. Courtesy, Persuade, Awe, Battle,Lore, Song, Inspire. And I am sure there are more skills that could be argued for it to work with.

I played a Noldor Elf with this trait, I didn't get a whole lot of use from the trait. But that doesn't mean you can't get some use from it. Like others have said you could use this trait to confirm your character's dedication to the free people's as a sworn enemy of the Sauron. So you could activate the trait for Courtesy, Persuade tests when speaking to other people who are sworn enemies. To convince any of the Wizards of your dedication, groups of Elves, Rangers, Beorn, Dwarves perhaps. As a loremaster I would let players activate the trait for the intimidate foe action, for an auto success or to gain AP.I would also rule that the character knows old lores about Suaron. They may be able to speak a bit of the black speech, and would understand much about the First Age when it came to Sauron, Morgoth, Balrogs, The corruption of Numenor, The creation of the Rings of Power. (Not how to create Rings of Power, but the history. I would let them use it for Batte tests. I would also let players use it with the Rally/Enhearten Comrades action.

So with all that said we already have a nice list of skills that the trait can be used with. Courtesy, Persuade, Awe, Battle,Lore, Song, Inspire. And I am sure there are more skills that could be argued for it to work with.

That's a great idea. I could see an auto-success (or an AP) for a preliminary Battle roll based on this.

Much of the "Lore" part would probably fall under the Shadow-lore trait. You might allow it if no other player has that trait in the group. Otherwise, I'd advise against allowing an Enemy of Sauron to be also a Lore Master.

It seems fitted for characters like Elladan and Elrohir, who are fierce fighters "in the field" against orcs and other foul creatures, but not so much wise counselors. They weren't present at the Council of Elrond, for instance.

Allowing for autosuccess and APs in Preliminary Battle tests, and Intimidate Foe tasks, seems good to me.
Also in Introductions when talking with people like Beorn or Gandalf, for example, it might work well.

As LM, I'd also try to make it come into play when engaging enemies: weak adversaries (goblins) would only attack the hero if they can swarm him (3 enemies engaging the hero) or from a distance. Also, great enemies (Orc Chieftain) would take preference on him over other heroes.

As a player, I'd buy the biggest shield and the thickest armour available right from character creation!